A Rapid and Accurate PCR-Based Method for Mating-Type Determination in the Heterothallic Oomycete Plasmopara viticola , the Causal Agent of Grapevine Downy Mildew

Plasmopara viticola is a heterothallic diploid oomycete responsible for grapevine downy mildew, one of the most damaging grapevine diseases worldwide. Since no rapid method for mating-type characterization of strains is currently available, mating-type identification must be performed through crossing assays, which are time-consuming. This study reports the development of two PCR-based molecular markers (MT_indel1 and MT_indel2) based on size variation to distinguish between the mating-type alleles of the oomycete P. viticola. For both markers, P1 strains (MAT-a/MAT-b) exhibited a double-band profile, whereas P2 strains (MAT-a/MAT-a) displayed a single PCR band. The markers were validated on a set of 37 reference strains collected across Europe and showed perfect concordance with mating-type phenotypes determined by crossing tests. They provide a robust, sensitive, and inexpensive DNA-based detection system for mating-type identification in P. viticola, offering valuable insights into the pathogen's reproductive biology and genetic diversity. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .